# operator<<,>>(std::mersenne_twister_engine)

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< cpp‎ | numeric‎ | random‎ | mersenne twister engine

template< class CharT, class Traits > friend std::basic_ostream<CharT, Traits>& operator<<( std::basic_ostream<CharT, Traits>& os, const mersenne_twister_engine& e ); | (1) | (since C++11)
template< class CharT, class Traits > friend std::basic_istream<CharT, Traits>& operator>>( std::basic_istream<CharT, Traits>& is, mersenne_twister_engine& e ); | (2) | (since C++11)

1) Writes the textual representation of the current state of e to os with fmtflags set to std::ios_base::dec | std::ios_base::left and the fill character set to the space character.
After writing, os's original fmtflags and fill character are restored.
2) Reads a textual representation of engine state from is (denoted as text) with fmtflags set to std::ios_base::dec, and sets the state of e to that state.
After reading, is's original fmtflags is restored.

- If text was not previously written using an output stream pr, the behavior is undefined.
- Otherwise, if any of the following values is false, the behavior is undefined:

  - is.getloc() == pr.getloc()
  - std::is_same<decltype(is)::char_type,
    decltype(pr)::char_type>::value
  - std::is_same<decltype(is)::traits_type,
    decltype(pr)::traits_type>::value

- Otherwise, if text is not a valid textual representation of any state of decltype(e), the state of e is unchanged and is.setstate(std::ios_base::failbit) is called.
- Otherwise, given another engine eng of the same type as e. If text was previously written by pr << eng and there is no intervening invocations of e or of eng between pr << eng and is >> e, e == eng is true.

These function templates are not visible to ordinary unqualified or qualified lookup, and can only be found by argument-dependent lookup when decltype(e) is an associated class of the arguments.

### Parameters

os | - | output stream to insert the data to
is | - | input stream to extract the data from
e | - | pseudo-random number engine

### Return value

1) os
2) is

### Complexity

1,2) \(\scriptsize O(n) \)O(n).

### Exceptions

2) May throw std::ios_base::failure when setting std::ios_base::failbit.

### Defect reports

The following behavior-changing defect reports were applied retroactively to previously published C++ standards.

DR | Applied to | Behavior as published | Correct behavior
--- | --- | --- | ---
LWG 3519 | C++11 | the form of insertion and extraction operators were unspecified | specified to be hidden friends

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